The present invention relates to a device to stop the penetration of a cranial drill that is used to pierce the skull during neurosurgical procedures. Many neurosurgical procedures such as ventriculoscopy and ventriculography procedures require the piercing or opening of the patient's skull to perform the procedure or to insert devices which measure pressure or to provide drainage. In these procedures, the skull is perforated with a cranial perforator or with a cranial drill. Cranial drills are usually twist drill bits which are secured to a manual hand operated drill or a power drill, either an electric or pneumatic drill.
Care must be exercised in the utilization of twist drills in drilling openings in the skull to prevent the drill from extending through the skull into the dura.
Drill stops of different types have previously been used in performing cranial surgery. Typical of these adjustable guards or stops to control the depth of penetration of cranial drilling instruments is that shown in U.S. Pat. No. 3,682,177. This patent discloses a manually operated drill with a twist drill point and an adjustable depth guard surrounding the drill bit. The depth guard is held in position by a coupling and a set screw.
Another drill guide and stop mechanism are shown in Ghajar U.S. Pat. No. 4,931,056. This patent discloses a drill guide which is a platform with legs arranged in a triangle which positions the drill guide over the drill entry point on the skull. There is a tube affixed to the platform into which the drill bit is inserted to guide the drill into position. A series of spacer rings are affixed to the handle of the drill bit which control the depth of the drill guide. The spacer ring contacts the top of the guide tube to limit the penetration of the drill bit into the skull.
The spacers can be either constructed as separate units or may be a single unit with perforated portions to break off to obtain the desired depth. The mechanism employed in the Ghajar drill is suitable only in connection with the base as the stops are not attached to the drill and are designed to butt against the top of the tubular drill guide which is affixed to the base of the device.
Another commonly employed drill stop is a circular bushing with a bore that is sized for the particular size drill bit. A set screw is used to lock the bushing to the drill bit and limit the effective drilling length and penetration of the drill bit.